9. Geert Boersma, Gravity, inertia and ether

During a long time, Newton’s ideas about gravity were widely accepted, although not all problems were solved. The main problem was that a body acts immediately on any other body. Immediately in two senses: without a (perceptible) medium and without time-delay. Before the relativity theory, ether was regarded as the medium, but this medium had no physical properties: it acted like a preferred coordinate system. The force acted without time-delay; a time-delay would give rise to an increase in energy. In the theory of relativity (GRT), the situation is even worse. Space–time can be seen as a medium, but there is still no time-delay in gravitation. Perturbations in space–time travel with infinite speed, much faster than the maximal speed that is allowed in GRT. The main problem is probably insufficient difference between nature—God’s Creation—and human abstractions. Space and time are not physical quantities, they can be chosen like coordinate systems. But the ether must be physical; the choice is a modification of Lorentz’s ether, with properties that have a resemblance with an elastic medium (ELET). Just like an elastic medium, the ether has two speeds for the travel of disturbances, one for transversal disturbances and one for longitudinal ones. Transversal disturbances travel with the speed of light, longitudinal disturbances travel much faster. Using Lorentz’s formulae for movements with respect to the ether, the movements of a body in a central gravitational field are calculated. For the bending of light and the perihelion advance the results are the same as for GRT. A main difference is that ELET gives no “black holes.” For a very concentrated energy the speed of light goes only asymptotically to zero, as the radius decreases. To get some insight in the distribution of the ether within the cosmos, the stresses in the ether are considered. The result is that the expansion rate of the ether is the same as that of the material cosmos. Therefore, there is no force between the galaxies, and the expansion rate of the cosmos is constant. For spiral galaxies, it is concluded that the rotation curves can be explained by rotation of the ether in the same direction as the stars. No dark matter is needed.